1. Field of the Invention
This invention relates generally to signals used in railway systems and more particularly to methods and apparatus for mounting the reflector and lamp receptacle of a signal to the signal housing.
2. Description of the Prior Art
Currently in the railroad industry, signals including those used at railroad-highway grade crossings are generally comprised of a reflector enclosed within a cast metallic housing. A lamp receptacle is also mounted within the housing that holds an incandescent electric lamp. The mounting for the incandescent lamp should allow the lamp to be positioned so that light from the lamp will be concentrated by the reflector and directed through an appropriately colored roundel. Thus, the intended observer of a signal will perceive the intended indication of the signal.
A typical prior art signal unit is shown in FIGS. 1 and 2. The reflector used in the signal units of the prior art is mounted to the as-cast surface of the housing. Pads of elastomeric material are placed between the reflector and the housing to compensate for discrepancies between the two components. The lamp receptacle is suspended from thin metallic bars or strips that in turn mount to as-cast surfaces of the housing. When these signals are built, the distance from the receptacle to the reflector must be manually adjusted for optimum light output. This often entails bending of the metallic strips and manipulation of the reflector. Such mounting means in the prior art signal are shown in prior art FIGS. 1 and 2.
Referring to FIGS. 1 and 2, a prior art highway crossing signal 5 generally comprises a parabolic reflector 7 enclosed within a suitably configured cast metallic case 6. A suitable door 8 contains a colored roundel 9; door 8 may be readily opened whenever access to the internal parts of the signal is required. An incandescent electric lamp 10 is located such that the filament of lamp 10 coincides with the focal point of reflector 7. Lamp 10 is retained by lamp receptacle 11, which is supported by suitably configured metallic strips 12. Insulating sleeving or tape 13 is placed between the lamp receptacle 11 and metallic strip 12 in order to electrically insulate the lamp receptacle 11 from the rest of the signal. This insulation is necessary to meet the insulation standards of the signaling industry. A cast metallic bracket 14 supports the entire lamp assembly. Elastomeric pads 15 are placed between reflector 7 and case 6. A single mounting bolt 17 is used to exert mounting pressure on reflector 7 through mounting plug 16, thereby compressing elastomeric pads 15 and retaining the reflector at the desired location.
When the signal unit 5 is assembled, it is necessary for the assembly personnel to bend the metallic strips 12 in order to position the lamp filament at the reflector focal point to obtain the best light output from the signal. This can be a time-consuming procedure. Also, tightening of bolt 17 can deform the reflector and impair its optical efficiency. Degradation of the elastomeric mounting pads 15 due to aging and weather conditions can cause shifting of the reflector 7, thus impairing the light output of the signal unit.